Induction coil



E. WARNKEN 2,459,605

INDUCTION COIL Jan. 18, 1949.

Filed Dec. 4, 1945 I N V E N TOR, E/mew Mfl/mm Patented Jan. 18, 1949INDUCTION COIL Elmer Warnken, Colerain Township, Hamilton County, OhioApplication December 4, 1945, Serial No. 632,676

4 Claims. 1

This invention relates to an induction coil and a method ofmanufacturing the same. The coil with which the invention is concernedparticularly, is one adapted for use in permeability tuning ofelectronic devices, or of other devices embodying tuning circuits.

An object of the invention is to provide a coil of the characterreferred to, which will enhance the efll'ciency of a tuning circuit byoffering very fine tuning characteristics and maximum control offrequency changes.

Another object is to provide a method of manufacture whereby theimproved coil may be produced rapidly and inexpensively, to the extentthat it may replace variable condensers in many instances and therebymaterially reduce the cost of electronic devices, while at the same timeincreasing the efiiciency and serviceability thereof.

A further object is to provide an improved induction coil for thepurposes stated, which is made mechanically rigid and durable withoutthe use of an interior supporting core or form.

Another object of the invention is to provide a coreless induction coil,the wire convolutions of which may be disposed in exceedingly closeproximity to an inner reciprocable metallic rod or slug, to gain theadvantages of fine tuning and control as above mentioned.

The foregoing and other objects are attained by the means describedherein and illustrated in the accompanying drawing, in which:

Fig. 1 is a side elevational view of an unmounted wire coil embodyingthe features of the invention.

Fig. 2 is a side elevational view, partly broken away, showing the coilmounted between a pair of end guides.

Fig. 3 is a side elevational view of a modification, part being brokenaway.

Fig. 4 is a side elevational view of a metallic rod or slug, andcounterbalance means therefor, whereby the rod or slug may be guided inits movement longitudinally through the hollow coil.

The practice heretofore followed in producing induction coils forpermeability tuning purposes, was that of winding the insulated coilwire upon a rigid hollow cylindrical form which became an essential partof the finished coil. The use of the cylindrical form was considerednecessary for the support of the wire-convolutions, due to the very fineor light gauge wire used in forming the coil. Such wire in fact is solight as to possess very little strength, and even less rigidity. Sincefor use in permeability tuning the coil was required to accommodate aclosely fitted straight metallic 2 rod or slug reciprocable lengthwisewithin it, the coil necessarily was maintained in a straight and rigidcondition by means of the cylindrical form. The form, however, in orderto impart the required strength and rigidity to the coil, had anappreciable wall thickness which limited the extent to which the slugcould approach the inside con olutions of the coil. This condition wasnot conducive to efllciency and sharp tuning of the circuit in which thecoil was connected, wherefore the aim of the coil designer has been todevise the thinnest possible form wall without sacrificing the strengthand rigidity required for proper support of the wire convolutions of thecoil. The limit in reducing the form wall thickness -"perently hase beenreached, and conseouently the efilciency of such coils has reached itslimit also.

In accordance with the present invention, the coil is made without aninterior form or core, with the result that maximum proximity of the rodor slug to the innermost convolutions of the coil can be achieved. Tomake such a careless coil serviceable, a special reinforcing treatmentis required in the fabrication thereof, as will be explained. Withreference to the drawing, 5 indicates the coil of very fine insulatedwire, the terminal ends of which are indicated at i and l. The coil iscylindrical in cross-section, and has an accurately formed anddimensioned inner surface I which is highly finished and smooth incharacter. The inside of the coil is adapted to snugly but slidablyreceive the metallic cylindrical slug 9, which is usually constructed ofpowdered iron pressed or molded to smooth rod formation. Since the coilis devoid of any inner core or form, the outer surface of the slug restsin very close proximity to the inner convolutions of the coil winding asthe slug is reciprocated longitudinally therethrough incident to thetuning operation.

In fabricating the coil 5, a smooth metallic mandrel or temporary form,cylindrical in crosssection, is first coated with a suitable wax orother releasing agent. and then is wound with fine insulated wire toform upon the mandrel a coil of any desired winding pattern. Eitherduring the winding operation or subsequently thereto, the winding is tobe impregnated or saturated with a resinous material or binder whichwill set or harden to an inert state without checking or cracking, Theresinous material or binder having been set or cured while the coilremains upon the mandrel, imparts to the coil the characteristics ofmechanical rigidity and hardness such that it may be stripped from themandrel and handled without liability to distort, bend or disintegrate.Due to the smoothness of the mandrel and the presence of the releasingagent upon it, the stripping of the coil from the mandrel is easilyaccomplished, with the coil leaving the mandrel accurately shaped anddimensioned to nicely accommodate a slug or rod such as Fig. 4illustrates. Application of heat to the waxed mandrel will generallyfacilitate and expedite the stripping operation.

The binder used in producing the coil is preferably a resin of a typewhich, when cured or set to the hardened state, will possess thequalities of high resistance to abrasion, moisture absorption, andcurrent leakage. It should also be resistant to checking or crackingupon setting, even when generously applied to the coil windings. Ahighly satistfactory material that may be used as the binder, is ahighly plasticized thermosetting phenol formaldehyde resin. A syntheticresin of this type is obtainable under the designation of P- 162, aproduct of The Ironsides Company, at Columbus, Ohio.

Various other binders which will set up to a hardened state, may beemployed with the attainment of satisfactory but generally lessdesirable results, among them being the thermoplastic resins, thecontact or monomeric resins, and asphaltic compounds or binders such asshellac, spar varnish, and enamels. The phenol formaldehyde resin,however, is more acceptable because of its high mechanical strength whencured to the inert state, and its disposition to cure in thick filmswithout cracking or checking. Should there be any tendency of the resintoward frothing or blistering during the curing cycle, the reaction maybe readily controlled with the use of defoaming agents or anti-skinningagents, examples of which are compounds of the class of capryl alcohol,and hexone.

As was stated previously herein, the binder may be applied either duringthe winding of the wire upon the mandrel, or subsequently thereto. Oneprocedure is that of passing the wire through a vat, spray, or otherapplicator of binding substance as the wire is fed to the mandrel. Tohasten setting of the binder, heat may be applied to the coated wirebefore it reaches the mandrel, or, if desired, heat may be played uponthe coil as the winding proceeds. Such treatment will serve to precurethe binder and hasten completion of the process.

As an alternative procedure, the insulated wire may be coiled upon themandrel prior to application of the binder material, and as a separatestep of the process the coil while remaining upon the mandrel may beimpregnated or saturated with binder material by dipping, spraying,coating or otherwise. Thereafter, the binder material may be set orcured to the hardened state by means of a baking or air-dryingtreatment, after which the coil may be stripped from one end of themandrel as a rigid self-sustaining unit accurately shaped anddimensioned as to its inner wall surface 8.

To prepare the coil for use as a permeability tuning device, it willpreferably be furnished with end guides such as are indicated at Illupon Fig. 2 of the drawing. These guides may be in the form ofcylindrical sleeves of insulating material applied to the opposite endsof the rigid coil, the internal diameter of each being the same as theinternal diameter of the coil. The necessary connection may be effectedbetween the coil ends and the sleeves, by shouldering or counterboringthe sleeves as at l2, and forcing them over the ends of the coils. Thesleeves may be cemented or otherwise secured in place upon the coil endsif necessary. The terminal ends of the coil winding may be projectedthrough holes in the sleeves (not shown).

Instead of applying the sleeves in the manner illustrated by Fig. 2,they may be applied in accordance with Fig. 3, wherein |3--l3 are plainsleeves of insulating material or the like endbutted at M to theopposite ends of the coil. These sleeves are of an internal diameterapproximating or conforming to the inside diameter of the coil, and maybe held in axial alignment therewith by means of a wrapper or adhesivesheet of paper, cloth, or similar flexible material covering theexterior surfaces of the sleeves and the coil, and serving as a retainerI5. The means of applying guide sleeves to the ends of the coil is amatter of immateriality to the invention, and is capable of considerablevariation in practice. The principal function of the sleeves is to lendsupport to the slug or rod 9 as it is reciprocated axially through thecoil from end to end thereof, or to a position at which the slug issubstantially withdrawn from the confines of the coil interior. The slugitself may be supported by means of small rollers l6 and I1 embracing anextension it of the slug. Movement of the slug or rod 9 axially of thecoil serves to change the frequency of the tuning circuit of which it isa part. Because of the fact that no supporting form or core is presentin the coil, the outer surface of the slug moves always in very closeproximity to the innermost convolutions of the coil, with the result ofattaining the finest possible tuning and accuracy of control. Thisresult is not merely a lineal phenomenon, but rather a logarithmicfactor which further enhances the behavior of the coil.

Computations and comparisons have proven that a gain in proximity of theslug area to the inside convolutions of the coreless coil has beenincreased by more than ninety percent, over the proximity characteristicobtainable with conventional coils wound upon plastic or paper cores orforms which remain within the coil. As a result of the presentconstruction, much finer tuning and better control have been assured inapplication of the improved coil to permeability tuning of electronicequipment.

What is claimed is:

1. As a new article of manufacture, an electric coil devoid of internalsupporting form comprising convolutions of insulated wire wound tohollow cylindrical formation, the convolutions thereof being fixedrelative to one another by a hardened binding material to render thecoil rigid and self-sustaining, notwithstanding the absence of astationary core, and a cylindrical sleeve of insulating material havingan internal diameter closely approximating the inside diameter of thecoil, fixed to an end of the coil in axial alignment therewith, theinnermost convolutions of the wire being included in the circumferenceof a coaxial imaginary cylinder which includes the inner surface of thesleeve.

2. A tuning device which comprises in combination, a coil of insulatedfine wire wound to hollow cylindrical formation, the coil being devoidof internal supporting form the convolutions of which are cementedtogether to impart rigidity to the coil, a cylindrical sleeve having aninternal diameter closely approximating the inside diameter of the coilfixed to an end of the coil in axial alignment therewith, the innermostconvolutions of the wire being included in the circumference of acoaxial imaginary cylinder which includes the inner surface of thesleeve and a metallic substantially cylindrical slug fitted within thecoil for reciprocating movement in the sleeve and in unobstructedrelationship to the innermost convolutions of the coil winding.

3. A tuning device which comprises in combination, a coil of insulatedfine wire wound to hollow cylindrical formation, the coil being devoidof internal supporting form the convolutions of which are cementedtogether to impart rigidity to the coil, a cylindrical sleeve having aninternal diameter closely approximating the inside diameter of the coilfixed to an end of the coil in axial alignment therewith, the innermostconvolutions of the wire being included in the circumference of acoaxial imaginary cylinder which includes the inner surface of thesleeve and a metallic substantially cylindrical slug fitted within thecoil for reciprocating movement in the sleeve and in physical contactwith the cemented inner convolutions of the coil winding.

4. As a new article of manufacture, an electric coil devoid of internalsupporting form comprising convolutions of insulated wire wound tohollow cylindrical formation, the convolutions thereof being fixedrelative to one another by a hardened binding material to render thecoil rigid and self-sustaining, notwithstanding the absence of astationary core, and a sleeve of an internal diameter closelyapproximating the inside diameter of the coil, fixed to an end of the 0coil in axial alignment therewith, the innermost convolutions of thewire being included in the circumference of a coaxial imaginary cylinderwhich includes the inner surface of the sleeve.

ELMER WARNKEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 824,048 Thomson June 19, 19061,372,850 Turney Mar. 29, 1921 1,409,352 Adair Mar. 14, 1922 1,587,252Hill June 8, 1927 ,643,998 Scott Oct. 4, 1924 1,674,934 Victo'reen June26, 1928 ,827,571 Fiene Oct. 13, 1931 1,874,723 Dawson Aug. 30, 19321,887,005 Apple Nov. 8, 1932 1,944,870 Apple Jan. 30, 1934 1,994,534Robinson Mar. 19, 1935 2,137,392 Cobb Nov. 22, 1938 2,245,373 Weiss June10, 1941 2,280,981 Schuh Apr. 28, 1942 2,298,275 Bohren Oct. 13, 19422,375,911 Foster May 15, 1945 FOREIGN PATENTS Number Country Date159,997 Great Britain Mar. 11, 1921 115,025 Australia Apr. 17, 1942

